Beam compass



Sept. 25, .1945. J. w. OEHRLI I 2,385,723

BEAM COMPAS S Filed -June 13,'1944 K 2 sheets-sheet 1 Y 25, :gh s 28 30 Fllz E. 3/

Sept.v 25, 1945. J'. w. oE|-.|R|

r BEAM COMPASS Y Filed June 15; 1'944 2 sheets-sheet 2v .f//J l R Zw@ .m1 m ..II N L i E.. H l 4 mf 4 24 2 2 .d .fl n A 1----I` .L l------- Patented Sept. 25, 1945 lOFFICE 2,385,723 BEAM coMPAss John W. oehrli, state college-Pa. Application June 13, 1944, serial No. 540,158

1o claims. (c1. 3er-160) This invention relates to beam compasses, and particularly to beam instruments having a movable trammel provided with a tilting control.

It has been recognized that in many instances there is a degree of resilience and lack of rigidityv in bow compasses and the like that make a beam compass an essential for certain uses. With this latter form of compass, however, successful use has been circumscribed by the fact that with a slidable bodily movable trammel point or the like, only rough adjustments can be made, while delicate, substantially micrometric adjustments are necessary but have not been provided and are not readily secured. When adjustments of refinement have been added to the control over the bodily trammel movement according to past practices, the instruments have been complicated, expensive, difficult to adjust, subject to undue wear making for inaccuracies, and possessed of such degree of resilience as to militate against the complete accuracy essential for proper use of the instruments.

' It is among the objects-of this invention; to provide a beam compass with a bodily movable trammel and separate means for securing minutely incremental exact and facile tilting control of the trammel point; to simplify the construction of beam Compasses; to provide a simple form of tilting control for a beam compass trammel; to provide a rotatable cam cooperating with a fulcrum on opposite sides of a beam for securing exact and relativelyfxed tilting adjustments of the trammel relative to the beam, which adjustment is maintained until manually changed by the operator; to provide a trammel with three points of gripping engagement of a beam which are arranged for adjustment for securing tilting control while maintaining substantially constant grip on thev beam; and many other advantages and objects of the invention will become more apparent as the description proceeds.

In the accompanying drawings forming part of this description:

Fig. 1 represents a side elevation of ai beam compass constructed in accordance withr one form of the invention, showing in respectively full and dotted lines two different positions of a trammel point in its tilting relation to the beam.

Fig. 2 represents a side elevation of the tilting sliding trammel of this'invention mounted on a beam, taken looking along lthe beam, according to the preferred form of invention.

Fig. 3 represents a longitudinal axial section of the tilting sliding trammel and beam of Fig. 2, taken transverselythereof, in a mid-'position of perpendicularity relative to the beam, with the beam in merely4 fragmentary section, and indicating irndotted lines the relative beam position in a position-of relative tilting of the trammel on li'ig. 4 .represents a fragmentary section throughthe elevation of Fig. 2 on line 4-4 thereofgon an exaggerated scale.

Fig. 5 representsa fragmentary elevation of a detail of the upper end of a trammel according to the preferred form of invention.

Fig. 6. represents a plan of the fragment of trammel shown in Fig. 5.

- Fig. .7 representsA a side elevation of a pivoted '1 sliding trammel according to -a modified Yform thereof, looking into the beam-receiving opening'thereof. i

Fig. 8 represents a longitudinal section through the modified form` of sliding tilting trammel shown in Fig. 7 with a fragment of beam shown in full lines in` one relatively adjusted tilting position of the beam and trammel.

' In' the preferred form of invention, shown in Figs. 1 and 2 and in detail in Fig. 3, a beam I0 is provided which is preferably substantially rectangular in cross section, having'lateraI parallel walls' or surfaces II and l2, andvupper and lower walls or surfaces respectively I3 and I4, and illustratively .maybe comprised of a deformed tube,

althoughif desired a solid rod maybe used. Preferably, the corners of the beam are slightly rounded instead of being completely sharply angular. In the beam shown in Fig. l; a reduced end I5 isformed for resilient interlock with an adjacent section of beam, if appreciable length greater than one beam is required. Usually the compass will include two or three different lengths of' beam, including a very short one for small arcs. On this' beam I0, when used as a compass, there are preferably two trammels, respectively, a primary trammel'II, and a secondary trammel I8. Primary trammel I6 is preferably of such length as tofurnish a grip for the'ngers and comprises preferably a mere trammel point II to be located at thecenter. of. rotation. Secondary trammel I8 is preferably rather short and carries the markingv element, whether it be another point, a pen, or the' pencil point 20 shown in Figs. 1,` 2 and 3. It will be Vunderstoodthat in using `the beam compass the trammels are suitably apertured as will be described and the leg or trammel lIv is first mounted on the beam at a convenient point toward-Tone end thereof,l and is preferably held tightly against undesired movement, andthe secondary trammel I 8 is mounted-and slid along the beam in a position of perpendicularity thereon, preferably, until the point or lead 20 is approximately on the mark for the desired arc. Then V all sliding stops, because such bodily trammel movement is not sufliciently certain and delicate and needs to be sharpened by the substantially Vernier movement incident to tilting in accordance with the invention. When the sliding stops with the secondary trammel approximately near the mark, then itis tilted as to bring the point 20 exactly on the mark. In moving through a succession of very close marks, tilting the secondary trammel can take care of the most minute changes.

In the preferred form of tilting trammel of either Vprimary trammel I6 or secondary trammel I8, a single tubular member 2| is provided having the transverse through aperture 22 formedV with the axial parallel side edges 23 and 2.4 arranged for close sliding fit with the parallel side Ywalls and I2 of the rectangular beam IU to` prevent wobble or oscillation about the longitudinal median axis of the beam l0, while the upper and lower surfaces of the slot have clearance from beam surfaces |3 and |4. Below the aperture 22,r

the tube 2| terminates in a skirt25l to receive with a tight push fit, the mechanism to be described. A pencil lead or point chuck element 2B at the inner end is flared to form the hollow cylindrical Y portion 21 arranged for anchored engagement within the skirt 25 of the main tube. Preferably, a mere tight machine fit will suffice to prevent relative motion between Ithese parts, although if desired they may be spot-welded or otherwise tacked together. The cylindrical end part of the chuck has an external shoulder 28 under the skirt Y, 25, and is threaded as at 30 to receive the com- 'pression collet 3| which constricts the lower portion of the chuck against the lead 20. 'I'he space.

within the cylindrical portion 21 houses a compression spring 32 working within the inner pe;-` riphery of a tubular extension 33 of a spring,-r

pressed conical follower fulcrum point 34Yhaving the axial aperture 35,.A vThe spring pressedconical fulcrum Vhas ,anl outer periphery 36 slidably guided in the skirt 25 vbelow the transverse slot or beam opening 2 2., and the spring 32 bears against the xed internal shoulder `3I of thechuck and Vthe 'inner shoulder formed by the conical end 34 to r,urge the spring pressed fulcrum axially toward thetransverse slot'22 and into contact with the. lower surface |4 of the beam IIJ when the latter. is in the slot 22. Preferably, the tube 2| isin-v dented to form an internal bulge or stop, not shown, for limiting the outward axial movement of the spring pressed fulcrum plunger 34. Above the upper limits. of -the slot 22, a ring 38 is anchored immovably on -the.tube'2|, in any desiredV manner, as by welding or brazing or the like, and

vouter surface of the tube 2| guided engagement with theflxed ring 3Ii1soV that the ycam'surface 43 changes `its position Vso thatits diametrically spaced high vpoint 45 and flow point 46 can reverse.

or` assume any desired 'diametrical complemental An annular camV 4| is f position. Preferably, as a simple means to prevent the cam 4| from dropping axially away from fixed abutment 38, its inner periphery 44 has a central peripheral groove 4'I into which a small bump 48 can be forced by a small tool directed through slot 22 before association of the beam ID therewith.

With the parts as thus far described, it will be clear that the secondary trammel I8 can be threaded easilyupon the-end of the beamk I0, as it simply requires a slightaxialgdepression of the spring plunger to suitably position the trammel and the beam. Note that the spring pressed plunger 34 exerts friction on the lower surface |4 of the beam, and also forces the upper surface I3 thereof against two substantially diametrically spaced points on cam surface 43, and establishes a frictional contact between the cam surface and Y of will engage two symmetrically disposed points It will remainl in such` on the cam surface 43. perpendicular relationdue tothe frictional constraint of the spring pressedplunger although still permitting predetermined sliding movements of the whole trammelA bodily along the beam.

This is for the rough adjustment, so to speak. Y

For making the final adjustment or for making progressive changes in the location of the point- 2 in the plane of the beam, the operators lingers very readily grasp Vthe knurled edge of the camv 4| and rotate same in either direction required so as to move the high point 45 toward one side or the other of the former mid-position transverse.

of the beam, to displace the symmetrical point engagement and establishY asymmetrical point engagement between the beam and cam surface re1- each side of the neutral mid-positionyvarying Vinative to the perpendicular of the axis of tube 2|', to gradually force the angular relation of the beam and trammel to change. It will beclear that this will be accomplished. by simultaneouslyY moving the wide portion of the cam to lie betweenv the beam and the xed planar guide surface ,49r

of the stop ring 33 on one side or the other of the neutral perpendicular relation, whileV also simultaneously moving the thinner portioncf the` cam between low point 43 and the guiding planar surface 40 of the fixed abutment on the other side of thev neutral perpendicular relation, to?

maintain constant` and uniform compensatory pressure on the beam on each side of the fulcrum point. This establishes consequently an ability to locate the point 28 anywhere in a wide; swing on just yields that required amount.` Thesimplicity,

utility and economy of the construction so far described will be obvious'.

It will be understood that, both trammels may be of the same constructioniif desired, and thereby very close disposition' of theaxial. point and the arc-marking device.willbefacilitated.4 For certain purposes, however,- t' may be desirable to` provide the form ofy device shownjnlig.Y l, at H5,4

in which the tube: 2|., otherwise identical with trammel |.8 of Fig. 3, is prolonge@ is ilattenedas at 49, and the end may be closed orleft open, preferably itis knurled.. Thev purposeiii-leavin,gvl

It will be 'clearz rotation of the knurled nut 63.

tube 2| open, at least far enough to permit the passage of a wire, is so that with the beam withdrawn, the wire can be forced into the aperture 35 to force out any pieces of broken lead that may have lodged in the chuck assembly.

It will be clear that the combination of elements on opposite sides of the beam comprising a fulcrum on one side of the beam in line with the axis, and the high and low points of the cam on the other side of the beam and of the axis of the tube of the fulcrum, furnishing a three-point grip of the trammel on the beam in all positions of adjustment fortilting, can find expression in other forms than the particular species disclosed in Fig. 3. For an illustrative modification incorporating the same control principle, reference may be made to the disclosure of Figs. '7 and 8. In this form, a shaft, illustratively relatively solid, as at 50, at the lower end terminates in a lead or point-gripping chuck element as 5I, carrying the threaded rotatable collet member 52 for tightening and controlling the grip on an illustratively combined point and lead 53. The shaft is axially and transversely bored as at 54 to removably house the inner end of the combined element 53, and is provided with a transverse beam-receiving bore 55 having the bottom sloping surfaces meeting or merging in the fulcrum ridges or knife edges 56 transversely formed by curved spaced shoulders or effective fulcrums at 51 and 58, upon which the corners formed by the intersection of the side walls Il and I2 with the lower surface I4 of the beam I0, rock in response to rolling change of pressure from the cam to be described. The vertical extent of the slot 55 is such as to receive and permit swinging of the beam to permit tilting of the trammel relative to the beam. The upper end of the body 50 is preferably tubular for lightness and is provided with the short axial recess Eil to receive the anchoring tongue 6I on the spring washer 62 forming the bearing surface for the cam to be described, and which inturn is adjustably forced against said cam by the knurled nut 63. A cam 64 having an upper planar surface 65 normal to the axis of the cam is mounted rotatably on the tubular extension of the body 50, with the upper guide plane in engagement with opposite convolutions of the spring washer 62, and wlth the planar cocked cam face 66 overhanging the upper end of the transverse slot 55 with the high side 61 and low side 58 arranged to engage the beam Il) and swing the beam and trammel relatively on the fulcrums 51 and 58, as in the preferred form. It will be evident, however, that in the instant form, the tension of the spring and, therefore, the frictional effect can be varied by The tension on the spring washer imparted by the nut 63 is a means for regulating the slidability and also the tilting ability of the trammel. With one tension the trammel slides freely and adjusts the same in tilting, but it may not be sufficiently fixed. It is perfectly possible to make the sliding bodily adjustment, then the tilting adjustment, before tightening the nut 64 and therefor tightening thefriction spring Washer, although it is preferred to establish-a degree of spring tension such as to permit restrained sliding, while permitting restrained but facile tilt adjustment. It will be observed that in moving from the mid-position of no tilt toward tilt in either direction, the line from the fulcrums 51 and 58 to the upper surface is very slightly increased. This may be desirable as it increases the friction toward the extremes of tilting while markedly diminishing it in the midposition. This serves as an indication of .trammel position and angle that is sometimes beneficial.

Having thus described my invention, Ivclaimz- 1. In beam Compasses, a trammel having a beam-receiving aperture with parallel lateral walls, a beam having parallel lside walls arranged to be received in said aperture and to have .a sliding engagement with the said yparallel walls to prevent relative rotation of the trammel or beam respectively about its longitudinal axis, said aperture having vertical clearance to permit relative swinging of the trammel and beam in the plane median of the two parallel walls, and means in the trammel engaging the upper and Alower surfaces of the beam for adjusting the relative angular positions of the beam and trammel in said median plane, said means fzomprising a rotatable cam mounted with its axis concentric with the axis of the trammel and having a sloping surface arranged to engage oneof the surfaces of the beam. y

2. In beam Compasses, aA trammel having a beam-receiving aperture with parallel lateral walls, a beam having parallel side walls arranged to be received in said aperture and to have a sliding engagement with the said parallel walls to prevent relative rotation of the trammel or beam respectively about its longitudinal axis, said aperture having vertical clearance to permit relative swinging of the trammel and beam in` the plane median of the two parallel walls, means in the trammel engaging theupper and lower surfaces of the beam for adjusting the relative angu-` lar positions of the beam and trammel in said median plane, said means comprising a rotatable cam mounted with its axis concentric with the axis of the trammel and having a sloping surface arranged to engage one of the surfaces of the beam, and fulcrum means on the opposite side of and in contact with the beam from the cam means with reference to which the beam and trammel effectively tilt as the cam is rotated.

3. In beam Compasses, a trammel having a beam-receiving aperture with parallel lateral walls, a beam having parallel side walls arranged to be received in said aperture and to have a sliding engagement with the said parallel walls to prevent relative rotation of the trammel or beam respectively aboutits longitudinal axis', said aperture having vertical clearance to permit relative swinging of the trammel and beam in the plane median of the two parallel walls, means in the trammel engaging the upper and lower surfaces of the beam for adjusting the relative angular positions of the beam and tram- `mel in said median plane, said means comprising a rotatable cam mounted with its axis concentric with the axis of the trammel and having a sloping surface arranged to engage one of the surfaces of the beam, fulcrum means on the opposite side of and in Contact with the-beam from the cam means with reference to whichy the beam` and trammel effectively tilt as the cam is rotated, and resilient means for urging the fulcrum 'and cam surfaces into relative gripping engagement of said beam.

4. In beam Compasses, a trammel having a beam-receiving aperture with parallel lateral walls, a beam having parallel side walls arranged to be received in said aperture and tohave a sliding engagement with the said parallel walls to prevent relative rotation of the trammel or beam respectively about its longitudinal axis, said aperture having vertical clearance to permit relative swinging of the trammel and beam in the plane median of the two parallel walls, means in the trammel engaging the upper and lower surfaces of the beam for adjusting the relative angular positions of the beam and vtrammel in said median' plane, said means comprising a rotatable cani mounted with its axis concentric with the axis of the trammel and having a sloping surface arranged to engage one of the surfaces of the beam, fulcrum means on the opposite side of and in contact with the beam from the cam means with reference to which the beam and trammel effectivelyswinging of the trammel and beam in the plane vmedian of the two parallel walls, means in the i trammel engaging the upper and lower surfaces of the beam for adjusting the relative angular positions of the beam andtrammel in said median plane, said means comprising a rotatable cam mounted with its axis concentric with the axis of the trammel and having a sloping surface arranged to engage one of the surfaces of the beam, fulcrum means on the opposite side of and in contact with the beam from the cam means with i reference to which the beam and trammel effectively tilt as the cam is rotated, and resilient means for urging the fulcrum and cam surfaces vinto relative gripping engagement of said beam,

said resilient means effective on' the cam means to cause it to frictionally engage the beam.

A6. In beam Compasses, a trammel having a beam-receiving aperture with parallel lateral walls, a beam having parallel side walls arranged to be received in said aperture and to have a sliding engagement with the said parallel walls to prevent relative rotation of the trammel or beam respectively about its longitudinal axis, said aperture having vertical clearancer to permit relative swinging of the trammel and beam in the plane s:

median of the two parallel walls, means in the trammel engaging the upper and lower surfaces of the beam for adjusting the relative angular positions of the beam and trammel in said medi an plane, said means comprising a rotatable cam I mounted with its axis concentric with the axis of the trammel and having a sloping surface arranged to engage one of the surfaces of the beam, fulcrum means on the opposite side ofv and in contact with the beam from the cam means with reference to which the beam andtrammel effectively tilt as the cam is rotated, resilient means for urging the fulcrum and cam surfaces into relative gripping engagement of said beam, said resilient means effective on the cam means to cause it to frictionally engage the beam, andV means adjustable to vary the tension of the` said resilient means.

7. A beam compass comprising a beam,.a trammel having a beam aperture to enable sliding of the trammel on the beam, fulcrum means on the trammel engaging one side of the beam, cam means on the ,trammel engaging the beam on a side opposite to that-engaged by the fulcrum and establishing with the fulcrum a substantial triangle of beam-gripping substantial points, and a single means operable to swing the thus created triangle gripping means from a positionof symmetry with the axis of the trammel to positions of asymmetry-therewith to adjust the trammel in a plane containing the beam and trammel.

8. In beam Compasses, a trammel having a beam-receiving aperture, a beam positionable in the aperture, means on one sidefof the aperture establishing a fulcrum for the trammel on said beam, rotatable means on said trammel for engaging the beam on the other side from said full crum, said rotatable meansy having a cam surface said fulcrum.v

9. In beam Compasses, atrammel having a beam-receiving aperture, a beam positionable in the aperture, means on one side of the aperture establishing a fulcrumV for the trammel on said beam, rotatable means onsaid trammel-for engaging the beam on the other side from said fulcrum, said rotatable means having a camv surface establishing a pair of spaced substantial lines of contact with said beam and arranged by rotation to swing the trammel relative to said beam about said fulcrum, means for varying the spaced relation of the fulorum and rotatable means to enable relative separation thereof to facilitate sliding of the trammel on the beam and for relatively closer positioning thereof for establishing a frictional engagement restricting relative sliding of the trammel on the beam. i

10. In beam Compasses, artrammel having a beam-receiving aperture, a beampositionable in the aperture, means on one side of the aperture establishing a fulcrum for the trammel on said beam comprising a first gripping member for the beam, rotatable means on said trammel for engaging the beam on the other side from said fulcrum comprising a second gripping member for the beam, said rotatable means having a cam surface establishing a pair of spacedcsubstantial lines of contact with said beam and arranged by rotation to swing the trammel relative tosaid beam about said fulcrum, and means for mounting one of the beam-gripping members in the trammel for resilient yielding as the rotatable means is adjusted. Y

JOHN W.r OEHRLI. 

